Driving a motor vehicle during dry, daylight hours is a relatively simple task requiring one to merely obey the traffic signals and keep the vehicle within the proper traffic lane as defined by the markings on the road. This relatively simple task becomes a particularly exasperating and often treacherous assignment, however, if darkness and wet weather conditions prevail. Under this scenario, the usual night driving handicap of reduced visibility is augmented by the wet weather conditions, thus making reflective road markings virtually imperceptible.
Road markings are generally made by using either hot or cold traffic stripe paint, cold tape, or more durable materials such as epoxy or thermoplastic. Road markings generally come in two forms. There are long line stripes and transverse stripes. Long line stripes are typically lines dividing lanes of a road or a path. Normally one applies one interrupted white line or two solid yellow lines. An interrupted line is a series of predetermined length traffic stripes separated by a series of predetermined length gaps. These interrupted lines and the solid lines are normally four inches wide. When two lines are applied, they are normally also separated by four inches. These dimensions do change, however, according to different county, state and city regulations.
In certain long line applications, one may also have a solid four inch line and an adjacent interrupted four inch line. These lines are generally separated by a four inch spacing. They are normally used in situations were a plurality of center turn lanes (i.e., left hand turn lanes in the United States) are used, for example, a three lane road.
Transverse lines are normally shorter markings or legends. Transverse lines are normally considered to be stop bars, crosswalks, railroad crossing markings, words such as "ONLY", arrows, symbols and other markings and legends of that nature. Since cars often come to stops on transverse markings, transverse lines are sometimes directly subject to the power applied to back wheels during acceleration of a motor vehicle. Thus, transverse lines generally undergo more wear than long line stripes. Consequently, transverse lines are normally thicker than long line stripes.
Generally when thermoplastic is used, stripes are usually applied in thicknesses of sixty to a hundred and twenty-five thousandths of an inch, and preferably, they are usually applied at ninety to one hundred and twenty-five thousandths of an inch. Also, it is preferable, but not necessary, to add reflective material on top of the traffic stripe in order to give the traffic stripe increased reflectivity at night. The reflective material primarily consists of glass beads which are applied on top of the traffic stripe after it is applied to the road surface.
Water does not drain from conventional road markings during wet weather conditions, however, and when it rains a thin film of water will form on top of the traffic stripe and thereby significantly reduce the retroreflectivity of the glass beads used therein. If a thick film of water forms on top of the traffic stripe, such as encountered in a heavy storm, the water will totally obscure the markings from view and thus make them totally ineffective.
As a result of the deterioration in traffic guidance which occurs during dark and wet driving conditions, the incidence of traffic accidents increases and the usual smooth flow of traffic is impeded. Attempts have been made to eliminate these dangers by providing individual raised reflectors on the road surface, by using large reflective elements in the road markings which protrude above the water film, and by forming profiled road markings which have thickened transverse portions projecting above the water film.
One of the most widely used marking systems in the United States is an individual raised reflector, such as that available under the tradename Stimsonite.RTM. 948 or that shown in U.S. Pat. No. 3,332,327. The reflector generally comprises an approximately four and one-half inch by two and one-half inch marker which is raised a one-half inch from the road and has sloped side surfaces. A reflective panel is disposed on each sloped side of the marker and the entire top surface is then covered with a plastic or glass coating. As an example, the individual markers are placed every forty feet or so, such that one hundred thirty two markers are used for each mile of road marking. The markers thus provide a raised reflectorized surface every forty feet or so to assist the motorist when driving during dark and wet weather conditions. The markers are put down by using an epoxy glue or an adhesive, however, there is still a problem with maintaining the markers on the road surface. For instance, on a hot summer day when the asphalt is especially soft, a heavy truck running over the marker will tend to push it into the asphalt below the surface of the road. Heavy trucks also tend to knock the markers up off of the road, thus leaving a hole where the marker used to be. Thus, in both instances, the effectiveness of the reflectorized marker is destroyed. The cost for such individual markers and their installation is also a significant drawback since utilization of the markers on top of road striping can increase the cost of road markings by four hundred dollars per mile, or more, dependent upon the spacing of the markers.
As an alternative to reflectorized markers, large glass beads have also been utilized to provide a profiled road marking have a pebble-like finish. In this system, produced by R.S. Clare & Co. Limited under the tradename Aquaflex.RTM., large one to four millimeter glass beads and small crushed stones are spread on top of a binder coat layer and then overcoated with paint. Smaller conventional reflective beads are then dispersed over the painted line. The portions of the large glass beads protruding above a water film on the road surface provide a reflective surface because they are covered with small reflective beads and the large glass beads themselves will also provide increased reflectivity to the road marking. Using this type of large glass beads substantially increases costs, however, and since the larger beads are not universally accepted for road marking, approval on a state by state basis is required. Further, because of their size, the large glass beads do not adhere well to the road marking and have a tendency to be dislodged by traffic.
A further marking system which is utilized primarily in Europe is generally described in U.K. Patent Application 2,121,462. This marking system uses a relatively thick striping material and a shaped die through which the striping material is extruded. The striping is applied in a line approximately one and one-half to three millimeters thick and every ten to fifty centimeters the die is raised to increase the outflow of the striping material and thereby form a wavy transverse ridge approximately five to ten millimeters thick. The striping material generally includes glass beads that are mixed therewith and additional glass beads are preferably sprinkled on top of the applied marking before it is completely hardened. Thus, the spaced ridges form a profiled marking having raised retroreflective surfaces at specified intervals which will project above the surface of a water film and thereby provide visible markings during dark and wet weather conditions. The glass beads covering the raised ridges, however, soon wear away due to the constant travel of traffic and, eventually, even the raised ridges themselves will wear down. Within a relatively short period of time, therefore, the increased visibility provided by the profiled marking is destroyed. In addition, the thickness of the marking prevents the water from properly draining from the road surface when the marking is applied as an edge line. This creates a pocket of standing water at the edge of the road surface which may cause vehicles to skid, thus leading to increased accidents.
A strong need therefore exists for a road marking having increased reflective properties such that it is visible at night during wet weather conditions, which is durable and economical to apply, and which allows for water drainage from the road surface.